The field of the present invention is material analysis and, in particular, methods and apparatus for evaluation of the properties of hydrocarbon fuels.
It is of great interest to be able to ascertain with specificity, among other properties, the octane rating and vapor pressure of hydrocarbon-based fuels. These fuels, such as gasolines, are typically formulated as blends of various components, and it is therefore of interest to be able to identify and quantify such components. These data are useful both during production of such fuels at the refinery and during delivery of such fuels to the end-user. In either case, with these data, the producer, for production control purposes, or the consumer, to meet engine requirements or for comparative purposes, can assess the quality or value of the product at hand. However, while the producer normally employs elaborate testing procedures to obtain such data, the end-user consumer is typically limited to trusting the rating posted at the pump.
Octane numbers are conventionally determined and stated according to several known ASTM methods. For example, a research octane number (RON) can be determined according to ASTM Method 2699-84, and a motor octane number (MON) can be determined according to ASTM Method 2700-84. In addition, the conventional pump octane rating is determined as one-half of the sum of RON plus MON.
Present fuel components which affect the octane rating and vapor pressure of hydrocarbon fuels include MTBE (an ether-based fuel enhancer), aromatics (such as benzene, toluene and xylene), and alcohols (such as ethanol and methanol). MTBEs typically have an octane rating of about 110, aromatics typically have an octane rating of about 105, and alcohols typically have an octane rating of about 114.
Therefore, by determining the presence and volume percent of these components in a conventional hydrocarbon fuel solution, the overall octane rating (along with other physical parameters such as vapor pressure of the fuel solution) can be determined.
Various methods are known for the evaluation of fuel properties. Conventional spectroscopy techniques enable sampling and evaluation of a fuel's components, but the equipment is both expensive and ordinarily not available for real-time, in-situ evaluation of a delivered product.
One method of evaluating fuel properties is known as near-IR spectroscopy, in which a sample is excited with light from a near-IR light source. Since known fuel components exhibit characteristic vibrational mode overtones when excited in the near-IR, the vibrations of unknown constituents can be evaluated and classified accordingly. The typical evaluative process is complex, involving substantial non-linear data comparisons. Kelly, et al, describe such a method in "Prediction of Gasoline Octane Numbers from Near-Infrared Spectral Features in the Range 660-1215 nm," Vol. 61, Analytical Chemistry, No. 4, p.313, Feb. 15, 1989, in which vibrational overtones and combination bands of CH groups of methyl, methylene, aromatic, and olefinic functions were observed in the near-IR spectral region of 660-1215 nm (15,150-8,200 wavenumbers). With the aid of multivariate statistical analysis, the spectral features were correlated to various fuel quality parameters, including octane number.
Maggard, U.S. Pat. No. 4,963,745 is an example of near infrared absorbance evaluation between 1200 and 1236 nm applied to the methyne band along with the tertiary butyl band, indicative of sources of free radicals which seem to lead to smooth combustion. The signal processing techniques used, however, are complex, including first, second, third, and fourth or higher derivative processing; division of absorbance at one wavelength by those at other wavelengths for noise reduction, spectral subtraction for absorbance differentiation; and combinations thereof, as well as various known curve fitting techniques, such as disclosed in Maggard, U.S. Pat. No. 4,963,745, which are incorporated herein by reference.
It is therefore an object of the present invention to provide a simplified method and apparatus for fuel property detection.
It is another object of the present invention to provide a relatively inexpensive, real-time, in-situ detection method and apparatus for detection of the properties of a hydrocarbon solution.
It is still another object of the present invention to provide a simplified method and apparatus for obtaining absorption data linearly relating to the quantity of components in a fuel solution and from which predicting fuel properties without complex mathematical processing techniques.